Foreign Affairs Minister John Baird acknowledged for the first time Monday the chances of reaching a “political solution” in Syria are becoming increasingly slim as the two-year conflict enters “a new dark chapter.”

The Conservative government has been extremely reluctant to discuss any type of military intervention in Syria, but reports of chemical weapon attacks last week have suddenly upped the ante and pressured the international community to respond.

The U.S., Britain and France have threatened retaliatory strikes in recent days, and leaders in those countries were in touch with Prime Minister Stephen Harper and Mr. Baird over the weekend.

John Kerry, the U.S. Secretary of State, said there was “undeniable” evidence of a large-scale chemical weapons attack in Syria, toughening the Obama administration’s criticism of Bashar al-Assad’s regime and outlining a justification for possible U.S. military action.

Last week’s attack was a “moral obscenity” that “should shock the conscience” of the world, he said at the State Department Monday.

“The indiscriminate slaughter of civilians, the killing of women and children and innocent bystanders by chemical weapons is a moral obscenity. By any standard, it is inexcusable and — despite the excuses and equivocations that some have manufactured — it is undeniable,” added Mr. Kerry, the highest-ranking U.S. official to confirm the attack in the Damascus suburbs activists say killed hundreds of people.

“This international norm cannot be violated without consequences.”

Officials said President Barack Obama has not decided how to respond to the use of deadly gases, a move the White House said last year would cross a “red line.”

But the U.S., along with allies in Europe, appeared to be laying the groundwork for the most aggressive response since Syria’s civil war began more than two years ago.

They appear to be considering a response that would punish Mr. Assad for deploying deadly gases, not sweeping actions aimed at ousting him or strengthening rebel forces.

Speaking to reporters in Toronto, Mr. Baird reiterated, “Canada believes the only way to halt the bloodshed in Syria is through a political solution.”

“However, we understand that this solution is becoming more and more difficult as the crisis enters a very dangerous new phase,” he added.

The foreign minister said the government was “incredibly outraged” over the apparent use of chemical weapons.

“Such an attack demands a firm response from the international community,” he said, adding Canada will work “in lockstep” with its allies.

However, the continuing international debate underscores scant appetite for a large-scale deployment of forces in Syria and the limited number of other options that could significantly change the trajectory of the conflict.

Meanwhile, a United Nations team already on the ground in Syria collected evidence from last week’s attack.

Despite coming under sniper fire, members crossed the front line to speak to doctors and victims.

Rebels said the UN officials were shot at from the final checkpoint before no man’s land between the two sides, manned by a pro-regime militia.

Five inspectors and their security team were travelling in seven vehicles on their way to Moadamiyat al-Sham, one of the sites where the opposition say more than 1,000 people were killed by poison gas.

“The attack was an attempt by Assad’s regime to intimidate the UN team and prevent it from discovering the truth about Assad’s chemical weapons attacks against civilians,” a statement from the opposition Syrian National Coalition said.

The regime blamed opposition “terrorists.”

The inspectors went ahead with the visit, spending several hours in makeshift hospitals taking samples and talking to doctors and survivors.

“I was on my way to call an ambulance [after the bombing],” one bearded man on a hospital bed was filmed saying.

“Suddenly I felt like everything went dizzy. I started shaking and throwing up. It went on for a minute and a quarter.”

Sergey Lavrov, the Russian foreign minister, maintained there was no proof suggesting the Assad regime was behind the chemical attack.

But Mr. Baird showed little doubt about the culprit.

“If you believe our Russian colleagues that this was somehow an act of the [rebels], the [Assad] government would have been very keen to get these inspectors in there as soon as possible,” he said.

The Syrian president has denied launching a chemical attack.

Postmedia News, with files from The Associated Press and The Daily Telegraph